Quantum chemical study of the nature of the ground state and the pressure-induced spin transition inCaFeO3

Abstract

Ab initio calculations have been performed to clarify the character of the electronic ground state of the high-temperature phase of $\mathrm{Ca}\mathrm{Fe}{\mathrm{O}}_{3}$ at different external pressures. The analysis of the correlated $N$-electron wave function of properly embedded $\mathrm{Fe}{\mathrm{O}}_{6}$ clusters in terms of optimal atomic orbitals clearly establishes the character of the ground state as being dominated by charge transfer configurations. For all pressures, the number of Fe $3d$ electrons is around 5 and iron should be considered as a ${\mathrm{Fe}}^{3+}$ ion. We find an $S=2$ to $S=1$ transition around $25\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ in the $\mathrm{Ca}\mathrm{Fe}{\mathrm{O}}_{3}$ crystal.